Resistor element



Dec. 14. 1926.

c. s. STEWARD ET AL RES I STUR ELEMENT Filed April 22 1925 gmww v n Xian ad 1 w 235,444 JQWW,

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Patented Dec. 14, 1926.

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CLARENCE S. STEWAR-D AND CHARLES F. BROWN, OF GHATTAINOOGA, TENNESSEE.

RESISTOR ELEMENT.

Application filed April 22, 1925. Serial No. 24,983.

This invention relates to new and useful in'iprovements in resistor elements, and more particularly to elements of small size appropriate for use in radio apparatus.

One of the objects of this invention is to provide a resistor whose initial resistance may be a: curately predetermined and adjusted, and which, when so constructed, has a stability and permanence of resistance which is independent and irrespective of atmos;

pheric conditions such as barometric pres sure, and is tree from disturbance by arcidental shock. Heretotore, resistor elements have been constructed for use in radio apparatus, but these elements have largely been.

subject to the difiiculty that their rcsistance could not be accurately predetermined, and when calibrated were subject to variations from day to day by reason of changing atmospheric conditions, and from moment to moment by reason of local conditions of the apparatus in which they were employed, and it dropped upon the floor, or tapped accidentally with a tool, would oftentimes permanently change their resistance. This resulted in poor operation of the set in which they were employed, since for use with vacuum tubes, it is essential that the resistance should not change within major limits, but must remain very close to the calibrated amount stated upon the label.

A further object is the provision of a re-.

sistor element in which the resistance may be accurately adjusted at the factory, and the resistor element held in this adjusted condition throughout its life.

.With these and other objects in View, we have represented on the accompanying drawings several forms of construction of this resistor element, but all embodying the same generic principle of stability and accuracy. In these drawings+ Figure l is a longitudinal section of a resistor element according to this invention;

Figures 2 and 3 are longitudinal sections of modified forms of construction; and

Figure 4 is section on an enlarged scale showing the relative dimensions of the plunger piston and the granules.

Referring particularly to Figural, we have shown a tube 1 of insulating material having the proper structural strength, such as lavite. We have found this material very suitable for our purpose, since it is substan tially free from any absorption or of permeation by the moisture of the atmosphere;

'sion.

and has also sufficient strength to receive screw threads and be subjected to a considerable strain both in compression and tenilt the ends of this-tube 1 are formed screw threads to receive interiorly screw of these'caps has an aperture to receive the threaded spindle i which has on its end, a plunger 5. The central bore through the sleeve 1 is indicated at 6, and'is made as near as possible circular and concentric with the outer periphery of the sleeve and with the caps 2, 2, so that the plunger 5 is carried substantially centrally within this here this screw threaded spindle a in adjusted position. An outer cap 8 is screwed or forced onto the closing cap 2 to provide smooth outer and end surfaces for making contact. \Vithin the bore hole 6 is placed a mixture-of conductive and non-conductive materials. After experimentation, we have found that the most suitable mixture for this purpose is comprised of finely divided lampblack and talc. These substances are mixed together in proper proportions as may be determined by experiment, to afiord substantially the desired resistance for the. crosssection and the length available between the plunger heads 5, 5 of the element. We prefer to have these materials so finely comminuted that they pass a two hundred mesh screen. It is obvious that as the proportion .oftalc relative to lampblack is increased, the resistance of a; given length of material of the same cross-section will be increased. I The plunger 51 is not constructed for a tight fit within the boreholefi, but'is made to fit somewhat loosely therein. The annular space thus afforded between the sleeve 1 and the plunger 5 should be of the order of a thousandth of an inch or less, that is,

less than the approximate diameters of the threaded caps 2, 2'1" The end wall 3 of each hole 6. A lock nut Tis provided for holding the small particles from passing the plunger 5, but does not prevent the free escape of all.

In constructing and assembling one of these elements, one cap and plunger as sembly is placed in position, and the mixture of lampblack and tale is placed in the borehole 6. The element is jarred and tamped during the process to obtain a fairly homogenou's and equally compressed mass. The

other end 'cap and plunger are then placed I oil, and the covering caps 8lplaced' in position.

We have found that if the plunger 5 fits tightly within the bore hole 6, the air contained within the mixture of lainpblack and tale is not permitted to escape, but apparentl-y tends to segregate in small bubbles which seriously affect the resistance-ofthe mass as 'awhole. In the courseof time, these bubbles may escape- The pressure upon and in.

the mass then changes, and the resistance no longer remains constant; thus preventing anyeasy calibration, and affecting the permanency of the) resistances constructed. Withour construction, however, the escaping air passes through the annular space ping will not change its resistance when once around the plunger head into the chamber about the spindle4, where ithas full op portunity to expand without aifecting vthe resistance. Obviously the escape of air may ockzurthrough the structure of-the plunger,

when perforated or permeable.

On the other hand, .the element is completelyshut off from the outer atmosphere, and is nobsubject to barometric variations. Since the powdery mixture is wholly en-' closed and held under firm pressure againstany shifting of position, blows or even dropadjusted.

It is obvious that b'y varyingthe composition ofthe mixture, resistancesmf any value from one hundred ohms to five; or ten meg-.- ohms may he provided within one and the same outer shell. 4 Although the above represents one formv of the resistance, which may' be called a cartridge form, since it resembles the ordinary cartridge fuse, and may be employed in a similar manner, it is obvious that other forms may be made by utilizing conical caps 8, or forms such as those shown in Figures 2 and 3. In Figure 2, the closing cap 12 carries the spindle 4 and lock nut 7 as before, but the spindle 4 is allowed to project a considerable distance to receive a clamping nut 13-for securing the end of a connecting wire 14. In Figure 3, the constructionis the same as in Figure 2, but the element may be employed in a cartridge fuse socket.

Having thus described our invention, what we claim is 1 I 1. In a resistor, a resistance composition comprising a mixture of finely divided lamp,-

black and talc.

.2. In a. resistor, a resistance composition comprising a mixture of finely divided lampblack and tale in a "compacted form.-

- 3. In a resistor, a resistance composition comprising a mixture of finely divided, and.

compacted lampblack and talc substantially free from air bubbles under pressure.

4:. I a resistor element, an insulatingtube having screw threads-onits exterior at each end, closing caps mounted on said screw threaded ends, screw-threadedspindles fitted through said caps, plungers on said spindles within said tube and aflording free escape to the air between said plungers and tube while holding the resistance composition in compacted condition, locking nuts to hold saidspindles in defined positionsand caps en-' closingsaid spindles and locking nuts.

.5. In a re istor element, an insulating tn-behaving screw threads on its exterior at each end, closing. capsfiinounted' on said screw-threaded ends, screw-threaded spin-.

d fitted through-:saidrefsd'plun ers on sgd spindles within tulle position in compacted condition.

tures.

CLARENCE s. sTiiWARn- CHARLES F. BROWN.

{HI I H and a ording" I v free escape to the air-between said plun'gers and tube while holding the resistance com- In testimony whereof, "we aflix our signa- 

